The control of parasitic infections in human and animal populations remains an important global endeavor. The causative organisms may be categorized as endoparasitic members of the classes Nematoda, Cestoidea and Trematoda or phylum Protozoa, or as ectoparasitic members of the phylum Arthropoda. The former comprises infections of the stomach, intestinal tracts, lymphatic system, tissues, liver, lungs, heart and brain. Examples include trichinosis, lymphatic filariasis, onchocerciasis, schistosomiasis, leishmaniasis, trypanosomiasis, giardiasis, coccidiosis and malaria.
The latter, ectoparasites, include lice, ticks, mites, biting flies, fleas and mosquitoes. These often serve as vectors and intermediate hosts to endoparasites for transmission to human or animal hosts.
While certain helminthiases can be treated with known drugs, evolutionary development of resistance necessitates a further search for improved efficacy in next generation anthelmintic agents.
The control of endo and ectoparasites, has long been recognized as an important aspect of human and animal health regimens. Traditional treatments were orally or topically administered and indeed such treatments are still in wide use. The more modern thrust of research, however, has been towards compounds which can be administered orally or parenterally to the animals and which will control endo and ectoparasitic populations by killing individual parasites when they ingest the blood of a treated animal.
Although a number of ectoparasiticides and endoparasiticides are in use, these suffer from a variety of problems, including a limited spectrum of activity, the need for repeated treatment and, in many instances, resistance by parasites. The development of novel endo- and ectoparasiticidic treatments is therefore essential to ensure safe and effective control of a wide range of parasites.
Published International Patent Application WO2001/076370 discusses anthelmintic compositions comprising a spirodioxepinoindole, particularly a paraherquamide or marcfortine derivative or analogue, and a macrocyclic lactone, particularly an avermectin or milbemycin derivative or analogue.
Combinations of agents, which are less prone to resistance, or which are active against a wider range of parasites are especially desired.